Tissue specific cell division inhibitors (chalones) have been well documented in the case of epidermis but evidence for other tissue chalones has been limited to one or two reports. Chalones have also been shown to inhibit cell division of neoplasias which originated from the same tissue source as the chalone. The potential application of chalones to the cure of cancer is our ultimate objective. First however it is necessary to obtain a supply of pure chalone, and develop an assay system that will eventually allow study of the mechanism of action of chalone in normal tissue. The immediate objective is to exploit the non-species specific nature of chalones in the development of the chick embryo assay. The tissues in chick embryos are in a state of controlled hyperplasia and with differentiation essentially complete by 15 days of incubation, they should be responsive to chalone. Our preliminary results with rat liver extract show this to be true. A tissue sensitivity spectrum of the chick embryo to extracts from a variety of adult rat tissues will establish the range of usefulness of this system. To shorten assay time more rapidly determined parameters such as inhibition of DNA synthesis will be explored. A variety of animal sources will also be explored to establish that best for large scale preparation of crude chalone. As assay techniques are improved, progress can be made on purification. Standard techniques of protein purification will be applied most of which are in routine use in this laboratory. These include: salt, ethanol or polyethylene glycol precipitation gel filtration, ion exchange chromatography and preparative electrophoresis. At least partial physical characterization (molecular weight, isoelectric point, sedimentation const., diffusion const., amino acid and non amino acid comp. etc.) of the chalone molecule will accompany purification. Where pure chalone is prepared in sufficient quantity, such factors as neoplasia cell division inhibition, both tissue specific and non-specific, and possible side effects on other tissues and mechanism in normal tissue will be studied in depth.